Exhaust systems for a combustion engine generally include a manifold connected to the combustion engine at one end and bolted to an exhaust pipe at the other end. The exhaust pipe extends a distance from the manifold and generally has a catalytic converter system bolted thereto. These catalytic converter systems generally include a ceramic substrate having a catalyst coated thereon and a metal housing surrounding the substrate. In general, the catalysts require a minimum temperature to react with the emissions and reduce them. Higher reaction temperatures enhance the removal of harmful emissions from the exhaust gases. The core temperature of conventional catalytic converters is typically 1,000 to 1,400° F. In automobile applications, the exterior surfaces of the catalytic converters are air cooled, rather than water-cooled, to a temperature of about 600 to 1,000° F. Such high temperature far exceeds the 200° F. set by the United States Coast Guard for the exterior temperature of the exhaust system of inboard or stern drive engines.
Although catalytic converters have been required in cars for many years, they have not been required in marine vessels with inboard or stern drive engines. However, in 2009, catalytic converters began being required by federal law in new marine vessels with inboard or stern drive engines. This requirement is challenging because it has been difficult to maintain a sufficiently cooled exterior temperature for marine applications while also maintaining a sufficiently high enough temperature in the element or core of the catalytic converter. The United States Coast Guard has a limit of 200° F. for the exterior temperature of the exhaust system of inboard or stern drive engines. The United States Environmental Protection Agency (“USEPA”) has emissions standards which require use of a catalytic converter in inboard or stern drive engines.
One known method of reducing the exterior temperature of the housing in which resides a catalytic converter for a marine vessel is to water cool the housing. This concept is disclosed in U.S. Patent Publication No. US 2009/0175772, published Jul. 9, 2009.
However, there is a need to maintain all exposed surfaces below the 200° F. limit by surrounding the exhaust manifold with liquid to cool the tubes containing the exhaust prior to these exhaust gases entering a liquid cooled catalytic converter.